Why Does Backing Up Your iPhone Take So Long?by Brian Flax
Backing up an iPhone can take a considerable amount of time, which varies depending on the amount of data you have and the number of times you've synced your device. The initial iTunes backup tends to take the most time, as this will be the first time that files are copied over to your computer and iTunes library. Backups will also have an extended duration when transferring large files such as images, video and music.
Backing Up Applications
The more applications you have on your iPhone, the longer the backup time will be. Itunes syncs all apps installed on your iPhone and all the data associated with each app. If you limit the amount of apps strictly to the ones you actually use, and make sure to remove those that are outdated or unnecessary, you'll cut down on the time it takes to backup and sync your device every time you connect it to your computer.
Sort Through Your Photos
If you're a heavy user of your iPhone's camera, a large library of image files will increase the time it takes to backup your device when connected to your iTunes library. Deleting these files on your iPhone after having transferred them to your computer's image library will speed up backups later. Before permanently deleting these files from your iPhone, it's important to make sure that these have successfully been added to your iTunes library by opening them on another device. You can always restore these to your iPhone later if needed on the go.
Review Your Media Files
In addition to photos, media files tend to increase the time it takes to backup a phone to your iTunes library. If you have videos or music on your iPhone that you no longer need, deleting these files will speed up the backup time. OS X Daily found that removing video files from the iPhone was the most effective in speeding up the backup process. iTunes video rentals can be fairly large in size and take a while to sync, so after viewing these, remove the files from your device permanently.
Keep Things Regular
IPhone backups can take more time when done infrequently, as more files and applications will accumulate on the phone. You can limit the time a backup takes by regularly syncing your iPhone with your iTunes library. It's good practice to backup your iPhone at least once a month, or whenever you've accumulated a large amount of images, videos or audio files. Keeping your backups regular can also help in the event your iPhone is lost, stolen or upgraded, since the files can be restored from your library back on to your device.